Benzodiazepines are frequently prescribed for elderly patients living in the community and for those in hospitals and institutions. Their use is more prevalent in women. Prolonged use of benzodiazepines is particularly likely in old age for the treatment not only of insomnia and anxiety, but also of a wide range of nonspecific symptoms. Long term users are likely to have multiple concomitant physical and psychological health problems. The distinction between benzodiazepine anxiolytics and hypnotics is difficult and somewhat arbitrary, since the differences between the compounds are less than their similarities, especially in respect of adverse reactions. Despite their wide therapeutic range, elderly patients are particularly prone to adverse reactions to benzodiazepines. The incidence of unwanted effects, predominantly manifestations of central nervous system depression, has been found to be significantly increased in hospitalised elderly patients, particularly in the frail elderly. Studies on unwanted effects during long term use are scarce, but there is some evidence of tolerance to side effects. However, benzodiazepines have been found to be frequently implicated in drug-associated hospital admissions. There is suggestive evidence that benzodiazepines, especially compounds with long half-lives, may contribute to the falls which are a major health problem in old age. The incidence of benzodiazepine dependence in elderly patients is unknown. The features of benzodiazepine withdrawal in the elderly may differ from those seen in young patients; withdrawal symptoms include confusion and disorientation which often does not precipitate milder reactions such as anxiety, insomnia and perceptual changes. Problems due to both adverse reactions and to benzodiazepine withdrawal may easily be overlooked in multimorbid elderly patients, particularly in those suffering from disorders of the central nervous system. There are numerous studies on benzodiazepine pharmacokinetics indicating that alterations, especially in distribution and elimination of certain compounds, occur in old age. Benzodiazepines with oxidative metabolic pathways and longer half-lives are likely to accumulate with regular administration. However, changes in pharmacodynamics may be more important to explain altered responses to benzodiazepines in the elderly. Although information on pharmacodynamics is still limited, there is convincing evidence of increased pharmacodynamic response in the elderly which may be further accentuated by disease factors. Since the variability of pharmacological response increases with age and is not always predictable, there is good reason at least to start therapy at lower doses and to titrate dosages individually. This may also be appropriate for the newer benzodiazepines, irrespective of advantageous pharmacokinetics.(ABSTRACT TRUNCATED AT 400 WORDS)